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CONTENTS
Volume 4, Number 5, September 2008
 

Abstract
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Key Words
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Address
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Abstract
This paper deals with civil infrastructures in general, sensor and smart structure technology, and smart steel structures in particular. Smart structures technology, an integrated engineering field comprising sensor technology, structural control, smart materials and structural health monitoring, could dramatically transform and revolutionize the design, construction and maintenance of civil engineering structures. The central core of this technology is sensor and sensor networks that provide the essential data input in real time for condition assessment and decision making. Sensors and robust monitoring algorithms that can reliably detect the occurrence, location, and severity of damages such as crack and corrosion in steel structures will lead to increased levels of safety for civil infrastructure, and may significantly cut maintenance or repair cost through early detection. The emphasis of this paper is on sensor technology with a potential use in steel structures.

Key Words
sensor; smart materials; smart structures; steel structures; structural control.

Address
Division of Civil, Mechanical and Manufacturing Innovation, National Science Foundation, 4201 Wilson Boulevard, Arlington, Virginia 22230, USA

Abstract
Recently, dense sensor instrumentation for structural health monitoring has motivated the need for novel passive wireless sensors that do not require a portable power source, such as batteries. Using a layer-by-layer self-assembly process, nano-structured multifunctional carbon nanotube-based thin film sensors of controlled morphology are fabricated. Through judicious selection of polyelectrolytic constituents, specific sensing transduction mechanisms can be encoded within these homogenous thin films. In this study, the thin films are specifically designed to change electrical properties to strain and pH stimulus. Validation of wireless communications is performed using traditional magnetic coil antennas of various turns for passive RFID (radio frequency identification) applications. Preliminary experimental results shown in this study have identified characteristic frequency and bandwidth changes in tandem with varying strain and pH, respectively. Finally, ongoing research is presented on the use of gold nanocolloids and carbon nanotubes during layer-by-layer assembly to fabricate highly conductive coil antennas for wireless communications.

Key Words
carbon nanotubes; layer-by-layer; nanocomposite; pH sensing; RFID; strain sensor; structural monitoring.

Address
The University of Michigan, Ann Arbor, MI 48109-2125, USA

Abstract
The ability of an electroactive polymer, IPMC (Ionic Polymer Metal Composites,) to produce electric charge under mechanical deformations may be exploited for the development of next generation of energy harvesters. Two different electrode types (gold and platinum) were employed for the experiments. The sample was tested under dynamic conditions, produced through programmed shaking. In order to evaluate the potential of IPMC for dry condition, these samples were treated with ionic liquid. Three modes of mechanical deformations (bending, tension and shear) were analyzed. Experimental results clearly indicate that IPMCs are attractive applicants for energy harvesting, with inherent advantages like flexibility, low cost, negligible maintenance and virtually infinite longevity. Besides, preliminary energy harvesting model of IPMC has been formulated based upon the work of previous investigators (Newbury 2002, Newbury and Leo 2002, Lee, et al. 2005, Konyo, et al. 2004) and the simulation results reciprocate experimental results within acceptable error.

Key Words
ionic polymer metal composites; energy harvesting; sensor model.

Address
Department of Mechanical Engineering, University of Nevada, Reno, NV 89557, USA

Abstract
This paper presents a feasibility study of flexible piezoelectric paint for use in wide-band low-profile surface-mount or embeddable ultrasonic sensor for in situ structural health monitoring. Piezoelectric paint is a piezoelectric composite with 0-3 connectivity. Because of its ease of application, piezoelectric paint can be readily fabricated into sensing element with complex pattern. This study examines the characteristics of piezoelectric paint in acoustic emission signal and ultrasonic guided wave sensing. A series of ultrasonic tests including pitch catch and pencil break tests were performed to validate the ultrasonic wave sensing capability of piezoelectric paint. The results of finite element simulation of ultrasonic wave propagation, and acoustic emission generated by a pencil lead break on an aluminum plate are also presented in this paper along with corresponding experimental data. Based on the preliminary experimental results, the piezoelectric paint appears to offer a promising sensing material for use in real-time monitoring of crack initiation and propagation in both metallic and composite structures.

Key Words
acoustic emission; crack; nondestructive evaluation; piezoelectricity; sensor; ultrasonic.

Address
Xin Li; Department of Civil & Environmental Engineering, Lehigh University, Bethlehem, PA 18015, USA
Yunfeng Zhang; Department of Civil & Environmental Engineering, University of Maryland, College Park, MD 20742, USA

Abstract
(Received August 15, 2007, Accepted March 3, 2008) Abstract: In this study, a real-time damage detection method using output-only acceleration signals and artificial neural networks (ANN) is developed to monitor the occurrence of damage and the location of damage in structures. A theoretical approach of an ANN algorithm that uses acceleration signals to detect changes in structural parameters in real-time is newly designed. Cross-covariance functions of two acceleration responses measured before and after damage at two different sensor locations are selected as the features representing the structural conditions. By means of the acceleration features, multiple neural networks are trained for a series of potential loading patterns and damage scenarios of the target structure for which its actual loading history and structural conditions are unknown. The feasibility of the proposed method is evaluated using a numerical beam model under the effect of model uncertainty due to the variability of impulse excitation patterns used for training neural networks. The practicality of the method is also evaluated from laboratory-model tests on free-free beams for which acceleration responses were measured for several damage cases.

Key Words
artificial neural network; output-only acceleration; real-time damage detection; structural health monitoring.

Address
Jeong-Tae Kim and Jae-Hyung Park; Department of Ocean Engineering, Pukyong National University, Nam-gu, Busan 608-737, Korea
Ki-Young Koo; Department of Civil & Environmental Engineering, Korea Advanced Institute of Science & Technology, Daejeon, Korea
Jong-Jae Lee; Department of Civil & Environmental Engineering, Sejong University, Seoul, Korea

Abstract
In bridge structures, damage may induce an additional deflection which may naturally contain essential information about the damage. However, inverse mapping from the damage-induced deflection to the actual damage location and severity is generally complex, particularly for statically indeterminate systems. In this paper, a new load concept, called the positive-bending-inspection-load (PBIL) is proposed to construct a simple inverse mapping from the damage-induced deflection to the actual damage location. A PBIL for an inspection region is defined as a load or a system of loads which guarantees the bending moment to be positive in the inspection region. From the theoretical investigations, it was proven that the damage-induced chord-wise deflection (DI-CD) has the maximum value with the abrupt change in its slope at the damage location under a PBIL. Hence, a novel damage localization method is proposed based on the DI-CD under a PBIL. The procedure may be summarized as: (1) identification of the modal flexibility matrices from acceleration measurements, (2) design for a PBIL for an inspection region of interest in a structure, (3) calculation of the chord-wise deflections for the PBIL using the modal flexibility matrices, and (4) damage localization by finding the location with the maximum DI-CD with the abrupt change in its slope within the inspection region. Procedures from (2)-(4) can be repeated for several inspection regions to cover the whole structure complementarily. Numerical verification studies were carried out on a simply supported beam and a three-span continuous beam model. Experimental verification study was also carried out on a two-span continuous beam structure with a steel box-girder. It was found that the proposed method can identify the damage existence and damage location for small damage cases with narrow cuts at the bottom flange.

Key Words
beam-like structures; deflection-based damage detection; modal flexibility; positive bending loads; outlier analysis; measurement noise; experiments.

Address
Ki-Young Koo; Department of Civil & Environmental Engineering, KAIST, 373-1, Gusong-dong, Yusong-gu, Daejeon, Korea
Jong-Jae Lee; Civil & Environmental Engineering, Sejong University, 98 Gunja-dong, Kwangjin-gu, Seoul, Korea
Chung-Bang Yun; Department of Civil & Environmental Engineering, KAIST, 373-1, Gusong-dong, Yusong-gu, Daejeon, Korea
Jeong-Tae Kim; Department of Ocean Engineering, Pukyong National University, 599-1 Daeyeon-dong, Namgu, Busan, Korea

Abstract
A new algorithm is proposed to determine optimal accelerometer locations (OAL) when a structure is identified by frequency domain system identification (SI) method. As a result, a guideline is presented for selecting OAL which can reflect modal response of a structure properly. The guideline is to provide a minimum number of necessary accelerometers with the variation in the number of measurable target modes. To determine OAL for SI applications effectively, the modal sensitivity effective independence distribution vector (MS-EIDV) is developed with the likelihood function of measurements. By maximizing the likelihood of the occurrence of the measurements relative to the predictions, Fisher Information Matrix (FIM) is derived as a function of mode shape sensitivity. This paper also proposes a statistical approach in determining the structural parameters with a presumed parameter error which reflects the epistemic paradox between the determination of OAL and the application of a SI scheme. Numerical simulations have been carried out to examine the proposed OAL algorithm. A two-span multi-girder bridge and a two-span truss bridge were used for the simulation studies. To overcome a rank deficiency frequently occurred in inverting a FIM, the singular value decomposition scheme has been applied.

Key Words
OAL; SI; MS-EIDV; FIM; mode shape sensitivity.

Address
Soon-Jung Kwon; Korail Research Institute, Korea Railroad Cooperation, Daejeon Government Complex, 139 Seonsa-ro, Seo-gu, Daejeon City, 302-701 Korea
Sungkwon Woo and Soobong Shin; Dept. of Civil Eng., Inha University, 253 Yonghyun-dong, Nam-gu, Incheon 402-751, Korea

Abstract
This paper proposes a practical and realistic method to establish an optimal lifetime maintenance strategy for deteriorating bridges by considering the life-cycle performance as well as the life-cycle cost. The proposed method offers a set of optimal tradeoff maintenance scenarios among other conflicting objectives, such as minimizing cost and maximizing performance. A genetic algorithm is used to generate a set of maintenance scenarios that is a multi-objective combinatorial optimization problem related to the lifetime performance and the life-cycle cost as separate objective functions. A computer program, which generates optimal maintenance scenarios, was developed based on the proposed method using the life-cycle costs and the performance of bridges. The subordinate relation between bridge members has been considered to decide optimal maintenance sequence and a corresponding algorithm has been implemented into the program. The developed program has been used to present a procedure for finding an optimal maintenance scenario for steel-girder bridges on the Korean National Road. Through this bridge maintenance scenario analysis, it is expected that the developed method and program can be effectively used to allow bridge managers an optimal maintenance strategy satisfying various constraints and requirements.

Key Words
bridge maintenance; optimum maintenance scenario; life-cycle performance; life-cycle cost; steel-girder bridges.

Address
Kyung Hoon Park and Sang Yoon Lee; Korea Institute of Construction Technology, 2311, Daehwa-dong, Ilsanseo-gu, Goyang, Korea
Jung Hyun Yoon and Hyo Nam Cho; Department of Civil and Environmental Engineering, Hanyang University, 1271, Sa 1-dong, Sangnok-gu, Ansan, Korea
Jung Sik Kong; Department of Civil, Environmental and Architectural Engineering, Korea University,
1, 5-Ka, Anam-dong, Seongbuk-gu, Seoul, Korea

Abstract
In the past 20 years, seismic isolation has see a variety of applications in design of structures to mitigate seismic hazard. In particular, isolation has been seen as a means of achieving enhanced seismic performance objectives, such as those for hospitals, critical emergency response facilities, mass electronic data storage centers, and similar buildings whose functionality following a major seismic event is either critical to the public

Key Words
seismic isolation; performance-based design; inter-story drift; floor spectra.

Address
University of California, 750 Davis Hall, Berkeley, CA 94720, USA

Abstract
Numerous devices exist for reducing or eliminating seismic damage to structures. These include passive dampers, semi-active dampers, and active control devices. The performance of structural systems with these devices has often been evaluated using numerical simulations. Experiments on structural systems with these devices, particularly at large-scale, are lacking. This paper describes a real-time hybrid testing facility that has been developed at the Lehigh University NEES Equipment Site. The facility enables real-time large-scale experiments to be performed on structural systems with rate-dependent devices, thereby permitting a more complete evaluation of the seismic performance of the devices and their effectiveness in seismic hazard reduction. The hardware and integrated control architecture for hybrid testing developed at the facility are presented. An application involving the use of passive elastomeric dampers in a three story moment resisting frame subjected to earthquake ground motions is presented. The experiment focused on a test structure consisting of the damper and diagonal bracing, which was coupled to a nonlinear analytical model of the remaining part of the structure (i.e., the moment resisting frame). A tracking indictor is used to track the actuator

Key Words
Oya Mercan, James Ricles, Richard Sause and Thomas Marullo; Department of Civil and Environmental Engineering, Lehigh University, 117 ATLSS Drive, Bethlehem, PA 18015, USA

Address
real-time hybrid testing; performance evaluation; elastomeric damper; seismic hazard reduction; servo-hydraulic control.

Abstract
This paper deals with the numerical model of a bracing-friction damper system and its deployment using the optimal slip load distribution for the seismic retrofitting of a damaged building. The Slotted Bolted Connection (SBC) type friction damper system was tested to investigate its energy dissipation characteristic. Test results coincided with the numerical ones using the conventional model of a bracing-friction damper system. The placement of this device was numerically explored to apply it to the assumed damaged-building and to evaluate its efficiency. It was found by distributing the slip load that minimizes the given performance indicies based on structural response. Numerical results for the damaged building retrofitted with this slip load distribution showed that the seismic design of the bracing-friction damper system under consideration is effective for the structural response reduction.

Key Words
bracing-friction damper system; slotted bolted connection type; slip load distribution; damaged building.

Address
Sung-Kyung Lee; Department of Architectural Engineering, Dankook University, Seoul, Korea
Ji-Hun Park; Department of Architectural Engineering, University of Incheon, Incheon, Korea
Byoung-Wook Moon, Kyung-Won Min and Sang-Hyun Lee; Department of Architectural Engineering, Dankook University, Seoul, Korea
Jinkoo Kim; Department of Architectural Engineering, Sungkyunkwan University, Korea

Abstract
(Receive June 16, 2007, Accepted November 15, 2007) Abstract. Long steel stay cables, which are mainly used in cable-stayed bridges, are easy to vibrate because of their low inherent damping characteristics. A lot of methods for vibration reduction of stay cables have been developed, and several techniques of them have been implemented to real structures, though each has its limitations. Recently, it was reported that smart (i.e. semi-active) dampers can potentially achieve performance levels nearly the same as comparable active devices with few of the detractions. Some numerical and experimental studies on the application of smart damping systems employing an MR fluid damper, which is one of the most promising smart dampers, to a stay cable were carried out; however, most of the previous studies considered only one specific control algorithm in which they are interested. In this study, the performance verification of MR fluid damper-based smart damping systems for mitigating vibration of stay cables by considering the four commonly used semi-active control algorithms, such as the control algorithm based on Lyapunov stability theory, the maximum energy dissipation algorithm, the modulated homogeneous friction algorithm and the clipped-optimal control algorithm, is systematically carried out to find the most appropriate control strategy for the cable-damper system.

Key Words
stay cable; smart damping system; semiactive control algorithm; MR fluid damper.

Address
Hyung-Jo Jung; Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and
Technology,373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea
Ji-Eun Jang; University of California, Santa Babara, Santa Babara, CA 93106, USA
Kang-Min Choi and Heon-Jae Lee; Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology,373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea

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